'73 Bronco Emissions Diagram

Can anyone supply a copy of the emissions diagram showing the pneumatic hose connections for a 1973 Bronco, 302 engine. This diagram was originally stuck somewhere in the engine compartment but is now gone. And Ford doesn't support this information.

Vac diagrams are difficult to come by. Correct vac diagrams are even more difficult to find (Al Gore hadn't invented the internet yet, back in '73). The thing is Ford had multiple configurations for each year depending on altitude, state produced for, transmission, etc. It would be relatively easy to tell you how to hookup each component, if we know what all you have.

This Bronco was sold in Colorado and used at 5000 feet elevation. I'm not all that familiar with the terminology, but I'll try to describe the system. The hose connections described here may be incorrect.

There's an EGR valve on the back of the carb. plate, a 3-port PVS valve on the coolant outlet, a similar 2-port valve on the heater supply line, a valve (I presume) on the transmission, a 2-port manifold vacuum source, and 2 vacuum ports on the 2 barrel Mortorcraft carburetor, one on front and one on the right side.

The current connections are as follows: line from manifold vacuum to the air cleaner valve; and a line from the manifold vacuum, thru the transmission valve, to the EGR valve. A T from this EGR line goes to the heater hose valve. The 2nd port of the heater hose valve goes to a four-way splitter connecting both carburetor vacuum sources with the top of the PVS valve. The bottom of the PVS valve connects to manifold vacuum and T's to the retard side of the distributor. The center port of the PVS goes to the distributor vacuum advance.

Most seems ok, except the two vacuum ports of the carb being connected together, and the manifold vacuum being T'ed to the carb vacuums. If you can comment on these connections, it would be appreciated. I could email a diagram if there's a way to email directly to you. My email is grrubin@earthlink.net

Thanks

Grubin said:

There's an EGR valve on the back of the carb. plate, a 3-port PVS valve on the coolant outlet, a similar 2-port valve on the heater supply line, a valve (I presume) on the transmission, a 2-port manifold vacuum source, and 2 vacuum ports on the 2 barrel Mortorcraft carburetor, one on front and one on the right side.

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Sounds good except for the valve on the transmission. Is it an automatic transmission? If so it's probably the vacuum modulator you're thinking of. Some had a single vac line to the modulator and some had two lines. The single line goes straight to manifold vac. The second line on the dual modulator is connected to the EGR in some way.

Grubin said:

The current connections are as follows: line from manifold vacuum to the air cleaner valve;

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Good. It should go to a bimetallic switch on the air cleaner to open or close the heat flapper depending on air temp.

Grubin said:

and a line from the manifold vacuum, thru the transmission valve, to the EGR valve.

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Sounds like the 2 port vac modulator.

Grubin said:

A T from this EGR line goes to the heater hose valve. The 2nd port of the heater hose valve goes to a four-way splitter connecting both carburetor vacuum sources with the top of the PVS valve.

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I don't know. Some years had a vacuum amplifier at the rear of the intake with 4-5 hoses connected to it.

Grubin said:

The bottom of the PVS valve connects to manifold vacuum and T's to the retard side of the distributor. The center port of the PVS goes to the distributor vacuum advance.

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This is consistent with the diagrams I've seen.

Grubin said:

Most seems ok, except the two vacuum ports of the carb being connected together, and the manifold vacuum being T'ed to the carb vacuums.

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This is definitely not correct. After looking at a bunch of diagrams on this site, http://www.mustangbarn.com/73vacuum.html, I've been able to break it down into two halves, EGR and vacuum advance. I couldn't find one single diagram that used all the components that you have but there are enough diagrams to get a real good idea of how they should be connected. I pieced this diagram together so that it shows the dual port advance and the EGR as you describe. I can't say that this is 100% correct. Maybe someone with a stocker will chime in.

Thanks for all of this. If there is a stock owner out there, it would be great to get a copy or description of the proper diagram.

Regarding your drawing, I don't see a spark delay valve ahead of my distributor, nor a dual area diaphram ahead of the EGR valve. Should I assume that the front carb port is what's labeled EGR port on your diagram? Also, does the 2 port vacuum modulator on the transmission go between the EGR port and the Temperature controlled vacuum valve? If so, is it directional? I don't really understand its function in the transmission.

It sounds like your opinion that the two carb ports should not be connected together; rather one to the distributor and one to the EGR system. Correct? Only concern is that there is a 4-way splitter linking those ports with the top PVS valve and the bottom of the Temperature controlled vacuum valve.

Thanks again for your help
Gary

That dual area diaphram is the vac modulator. As I recall the spark port is on the pass. side of the carb.

No I don't think the carb ports should ever be connected together. There's a pic of the vac amplifier in this thread. http://classicbroncos.com/forums/showthread.php?t=122652&highlight=vac*+amplifier